The life-shortening and carcinogenic effects of ionizing radiation have been reported from previous mortality studies of radiologists and other specialists. The non-concurrent prospective study of physicians suggested that the risk of cancer is still increased in radiologists as compared to other specialists despite the decreased dose of radiation to which they have been exposed in recent years. Further studies of the mortality in this population may indicate whether this trend is continuing among the recent entrants into the specialty. The proposed research will also attempt to identify dose levels of radiation and other toxic agents to which the various specialty groups are exposed and to relate these data to cause-specific mortality.